Report of the Benchmark Workshop on Plaice (WKPLE), 23–27 February 2015, ICES Headquarters, Copenhagen, Denmark

Stock identification issues were examined for three of the four stocks: based on larval drift,  otolith  characteristics,  genetics,  and  tagging  studies  the  Skagerrak  stock  was  evaluated to have strong connectivity to the North Sea plaice stock. North Sea plaice are having extensive feeding migrations into Skagerrak. The likely magnitude of the stock  mix  was  considered  sufficient  to  recommend  and  approve  that  plaice  in  the  North  Sea  and  Skagerrak  are  combined  and  assessed  as  one  stock  although  some  stock components in Skagerrak are considered resident. Given the size of the fishery in Skagerrak (about one tenth of the North Sea) the addition of catches from Skager-rak to the North Sea assessment has little impact on the combined assessment. For the combined North Sea and Skagerrak stock, future attempts should be made to include the  IBTS  data  since  it  seemed  to  improve  the  quality  compared  to  the  IBTS  data  which  excluded  the  Skagerrak  region.  In  addition  monitoring  the  Skagerrak  propor-tion  should  be  a  high  priority  for  the  North  Sea  stock  assessment  and  advice.  This  should be done to avoid local depletion of the resident stock.